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Code Issues Releases Wiki Activity

perf: avoid extra work in read_vc() (#5527)

This commit is contained in:
Charles Kerr 2023-05-14 15:01:04 -05:00
parent 04b5329345
commit edcddd00dd
2 changed files with 18 additions and 8 deletions
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21
libtransmission/handshake.cc
View File

@ -240,27 +240,32 @@ ReadState tr_handshake::read_vc(tr_peerIo* peer_io)
auto const info_hash = peer_io->torrent_hash();
TR_ASSERT_MSG(info_hash != tr_sha1_digest_t{}, "readVC requires an info_hash");
// find the end of PadB by looking for `ENCRYPT(VC)`
auto needle = VC;
auto filter = tr_message_stream_encryption::Filter{};
filter.encryptInit(true, dh_, info_hash);
filter.encrypt(std::size(needle), std::data(needle));
// We need to find the end of PadB by looking for `ENCRYPT(VC)`,
// so calculate and cache the value of `ENCRYPT(VC)`.
if (!encrypted_vc_)
{
auto needle = VC;
auto filter = tr_message_stream_encryption::Filter{};
filter.encryptInit(true, dh_, info_hash);
filter.encrypt(std::size(needle), std::data(needle));
encrypted_vc_ = needle;
}
for (size_t i = 0; i < PadbMaxlen; ++i)
{
if (peer_io->read_buffer_size() < std::size(needle))
if (peer_io->read_buffer_size() < std::size(*encrypted_vc_))
{
tr_logAddTraceHand(this, "not enough bytes... returning read_more");
return READ_LATER;
}
if (peer_io->read_buffer_starts_with(needle))
if (peer_io->read_buffer_starts_with(*encrypted_vc_))
{
tr_logAddTraceHand(this, "got it!");
// We already know it's a match; now we just need to
// consume it from the read buffer.
peer_io->decrypt_init(peer_io->is_incoming(), dh_, info_hash);
peer_io->read_bytes(std::data(needle), std::size(needle));
peer_io->read_bytes(std::data(*encrypted_vc_), std::size(*encrypted_vc_));
set_state(tr_handshake::State::AwaitingCryptoSelect);
return READ_NOW;
}

5
libtransmission/handshake.h
View File

@ -249,6 +249,11 @@ private:
using vc_t = std::array<std::byte, 8>;
static auto constexpr VC = vc_t{};
// Used when resynchronizing in read_vc(). This value is cached to avoid
// the cost of recomputing it. MSE spec: "Since the length of [PadB is]
// unknown, A will be able to resynchronize on ENCRYPT(VC)".
std::optional<vc_t> encrypted_vc_;
///
static constexpr auto DhPoolMaxSize = size_t{ 32 };